Chronic liver diseases are a serious health problem worldwide. One of the frequently reported glycan alterations in liver disease is aberrant fucosylation, which was suggested as a marker for noninvasive serologic monitoring. We present a case study that compares site specific glycoforms of four proteins including haptoglobin, complement factor H, kininogen-1, and hemopexin isolated from the same patient. Our exoglycosidase-assisted LC–MS/MS analysis confirms the high degree of fucosylation of some of the proteins but shows that microheterogeneity is protein- and site-specific. MSn analysis of permethylated detached glycans confirms the presence of LeY glycoforms on haptoglobin, which cannot be detected in hemopexin or complement factor H; all three proteins carry Lewis and H epitopes. Core fucosylation is detectable in only trace amounts in haptoglobin but with confidence on hemopexin and complement factor H, where core fucosylation of the bi-antennary glycans on select glycopeptides reaches 15–20% intensity.
These protein-specific differences in fucosylation, observed in proteins isolated from the same patient source, suggest that factors other than up-regulation of enzymatic activity regulate the microheterogeneity of glycoforms. This has implications for selection of candidate proteins for disease monitoring and suggests that site-specific glycoforms have structural determinants, which could lead to functional consequences for specific subsets of proteins or their domains. Introduction N-Glycosylation sequons of proteins (Asn-Xaa-Ser/Thr, where Xaa is any amino acid except proline) typically carry a diverse repertoire of structures, called glycan microheterogeneity. The diversity of protein glycosylation is influenced by the activity of many enzymes involved in the N-glycan biosynthetic machinery. Programa Para Hackear Redes Wifi Con Iphone 3gs on this page. , The source and the location of the glycoproteins also strongly influence the final glycan structure and site specificity. Microheterogeneity of protein N-glycoforms changes significantly in cancer diseases often in connection with changes in the activity of enzymes involved in N-glycoprotein synthesis. − One of the best documented examples of aberrant glycosylation is the progression of liver disease to hepatocellular carcinoma (HCC)., In the case of liver disease, changes in protein N-glycosylation can be analyzed efficiently by serologic monitoring of liver-secreted glycoproteins. − Reported changes of N-glycan repertoire in cancer include the formation of bisecting glycans with one molecule of N-acetylglucosamine attached via β1–4 bond to the branched core mannose, asialo and agalacto glycans, truncated structures with terminal galactoses or N-acetylglucosamines, (poly)- N-acetyllactosamines with beta 1–6 branching, and fucosylated glycans with fucose attached mainly at the C-3 position of outer arm N-acetylglucosamine or less frequently at the C-6 N-acetylglucosamine of the N-glycan core.